The present invention relates to file systems and more particularly to mirroring files between at least two storage devices.
In many applications of data storage systems, reliability and availability are critical performance issues. For example, in a retail solution, availability of a data processing system to process retail transactions may be essential. In such systems where reliability and availability are critical performance issues, mirroring of storage devices, such as hard drives or the like, may be beneficial. Mirroring storage devices may be carried out by replicating files on one storage device onto another storage device.
As an example of a mirrored file system, the 4690 Point-of-Sale operating system available from International Business Machines Corporation of Armonk, N.Y., provided a proprietary operating system for the retail environment. File mirroring operations could be provided in such a proprietary operating system by providing a file mirroring kernel which performed the mirroring operations. Such a kernel generally had complete access to the data of a storage device and would cause duplicate file operations to be performed for file operations to a preselected drive. Such control of the mirrored file system could be provided because of the close linkage between the proprietary operating system and the file mirroring kernel.
Furthermore, because of the purpose-specific nature of the proprietary operating system, a simple file access system could be provided with minimal concerns for security and control of access to files by behaved processes. However, in a more general purpose environment, such as systems utilizing general purpose multi-user operating systems such as WindowsNT from Microsoft Corporation, Redmond, Washington or Unix, AIX from International.Business Machines Corporation, Armonk, N.Y., Solaris from Sun Microsystems, Palo Alto, Calif. or Linux, concerns over security and file access may make the mirroring of files more complex.
Files in such general purpose systems generally have a set of permissions associated with them which are controlled by an xe2x80x9cownerxe2x80x9d of the file. The owner is, typically, the user or process which created the file. The set of permissions may be quite complex and vary from file to file. For example, certain of these permissions may make a file xe2x80x9cinvisiblexe2x80x9d or undetectable to other users or processes which do not have the appropriate set of permissions. As such, a mirroring process may be unable to detect the presence of certain files or be unable to read files in order to mirror the file to a secondary storage device. Also, the owner of a file may change its permissions and, thus, make a file which was once detectable, undetectable.
As described above, on a general purpose operating system, a mirroring process executing on a primary system may be unable to detect or read files if it does not have the proper set of permissions to access the files. Thus, the mirroring process may be unable to mirror the files from the primary data storage device to a secondary data storage device. Furthermore, a failure to mirror such files may be difficult, if not impossible, to detect prior to occurrence of a failure as the mirroring process may have no indication that a file exists and, therefore, may not know that it has failed to mirror the file. Such a failure to mirror critical files may be catastrophic in a system failure condition where operations are transferred to a data processing system associated with the secondary storage device. In such a case, the files needed to resume operations may be missing and the transfer of operations may be impossible.
In light of the above discussion, a need exists for improvements in file mirroring systems.
Embodiments of the present invention include methods, systems and computer program products which may provide access to files which are mirrored between at least a first storage device and a second storage device by determining if an access of the first storage device is by a process for mirroring files between the first storage device and the second storage device and assuming a privileged user level for the process for mirroring files so as that the access to the first storage device is performed at the privileged user level if the access is by the process for mirroring files. By assuming a privileged user level, the process for mirroring files may have access to the files to mirror, preferably, irrespective of the permissions assigned to a file by the owner of a file.
Furthermore, such access may be selectively provided so that the privileged user level is only provided to the process for mirroring files if the access is of a file to be mirrored. Thus, the assumption of a privileged user level may provide access to the files which are to be mirrored without privileged user access being provided for all files.
In particular embodiments of the present invention, the process for mirroring files may be registered with a file access system associated with the first storage device. The privileged user level for the process for mirroring files may then be assumed if the access is by the process for mirroring files and the process for mirroring files is registered.
In still further embodiments of the present invention, an access type associated with the access to the first storage device may be determined. The privileged user level may then be selectively assumed for the process for mirroring files based on the type of the access to the first storage device and if the access is by the process for mirroring files.
Furthermore, the assumption of the privileged user level may be accomplished by determining if a communication with a file system associated with the first storage device is from the process for mirroring files. A user level for the communication may then be set to the privileged user level if the communication is from the process for mirroring files. Thus, in particular embodiments, the communication with the file system associated with the first storage device may be intercepted and the communication modified so as to include a specification of the privileged user level so as to provide a revised communication. The revised communication may be forwarded to the file system associated with the first storage device.
In particular preferred embodiments of the present invention, a user level field of a data structure associated with the communication may be set to specify a root user level, such as 0.
In still further embodiments of the present invention, the first and second storage devices may be associated with a general purpose multi-user operating system. In such a case, the privileged user level may have a set of file access permissions associated with a user of the general purpose multi-user operating system. Preferably, the general purpose multi-user operating system is a Unix-type operating system. In particular, the Unix-type operating system may be Unix, AIX, Solaris and/or Linux.
In distributed embodiments of the present invention, the first storage device may be associated with a first data processing system and the second storage device may be associated with a second data processing system different from the first data processing system.
In still further embodiments of the present invention, a file mirroring system is provided. The file mirroring system may include a primary storage device, a mirrored storage device and a file system configured to control the primary storage device. A mirror process associated with the primary storage device may be configured to mirror files from the primary storage device to the mirrored storage device. A file access kernel may be configured so as to intercept communications with the file system, replace a user level associated with intercepted communications from the mirror process with a privileged user level and provide the communication with the replaced user level to the file system to access the primary storage device. The file access kernel may be further configured to selectively replace the user level of a communication from the mirror process.
In further embodiments of the file mirroring system, the primary storage device is part of a first data processing system and the mirrored storage device is part of a second data processing system. The file system may also be a file system of a general purpose multi-user operating system. The general purpose multi-user operating system may be a Unix-type operating system.
While the invention has been described above primarily with respect to method aspects of the invention, both systems and/or computer program products are also provided.